In communication devices, impedance mismatching between a coaxial connector which a signal is inputted in and outputted from and a printed board does not matter in a transmission speed of around 10 to 25 Gbps. At a transmission speed of around 40 to 60 Gbps, however, even small floating capacitance at a pad portion between the coaxial connector and the printed board may be a factor which deteriorates transmission characteristics of devices.
As a technology to reduce harmonic noises in transmitted signals, Patent Literature 1 discloses a technology related to a multilayer printed board having a conductor via which is not connected to any one of a signal layer, a ground layer and the other layers and having desired frequency band rejection characteristics for inputted signals.